The invention relates to active acoustic attenuation systems, and provides overall system modeling.
The invention particularly arose during continuing development efforts relating to the subject matter shown and described in U.S. Pat. No. 4,677,676, incorporated herein by reference. The invention also arose during continuing development efforts relating to the subject matter shown and described in U.S. Pat. Nos. 4,677,677, 4,736,431, 4,815,139, and 4,837,834, incorporated herein by reference.
Active attenuation involves injecting a canceling acoustic wave to destructively interfere with and cancel an input acoustic wave. In an active acoustic attenuation system, the output acoustic wave is sensed with an error transducer such as a microphone which supplies an error signal to a control model which in turn supplies a correction signal to a canceling transducer such as a loud speaker which injects an acoustic wave to destructively interfere with the input acoustic wave and cancel same such that the output acoustic wave or sound at the error microphone is zero or some other desired value. The acoustic system is modeled with an adaptive filter model having a model input from an input transducer such as a microphone, and an error input from the error microphone, and outputting the noted correction signal to the canceling speaker. The model models the acoustic path from the input transducer to the output transducer.
In one aspect of the present invention, a second model models the overall acoustic path from the input transducer to the error transducer, including the portion of the path from the input transducer to the output transducer and also including the portion of the path from the output transducer to the error transducer. The second model has a model output combined with the output of the error transducer to provide an error signal to the error input of the second model.
In another aspect, a third model models the speaker transfer function and the error path. The third model has a model output combined with the model output of the second model to provide a second error signal, which second error signal is combined with the first error signal from the error transducer to yield a third error signal which is provided as the error signal to the error input of each of the second and third models.